Slot machines are provided with a plurality of reels that are rotatably disposed and have a plurality of types of symbols marked on peripheral surfaces thereof. When a predetermined game value (for example, credits or the like) is betted and a predetermined operation (for example, an operation of a start button or a start lever) is performed, symbols are variably displayed in accordance with rotation of the reels. Generally, a bet of a game value is placed for pay lines defined over the plurality of the reels or all the symbols stopped to be displayed on the plurality of the reels.
When a predetermined time elapses after the symbols are variably displayed, symbols of each reel are stopped to be displayed on the basis of the result of an internal lottery. Then, an award on the basis of a combination of the symbols stopped to be displayed and the content of the bet is provided to a player.
Other than the above-described mechanical slot machines, there are video slot machines that use video reels for simulating mechanical reels. The video slot machines represent video reels by variably displaying symbol arrays including a plurality of types of symbols on a display device. In the video slot machines, as in the mechanical slot machines, symbols are variably displayed by using the video reels, and an award on the basis of a combination of the symbols stopped to be displayed and the content of the bet is provided to the player.
As described above, in the slot machines, an award is provided to a player on the basis of the combination of symbols and the content of the bet. As the content of the award, for example, a game value may be given as an award or a chance for participating in a special game, which is performed in a state more advantageous to the player than that of a base game, may be provided.
An example of thus configured slot machine for providing a change for participating in a special game as the content of the award is disclosed in U.S. Pat. No. 7,037,191 B2.
In the slot machine disclosed in the document U.S. Pat. No. 7,037,191 B2, symbols are variably displayed by using five reels, and, after a predetermined time elapses, symbols determined by an internal lottery are stopped to be displayed. Then, an award on the basis of the symbols stopped to be displayed is provided to the player.
In the slot machine disclosed in the document U.S. Pat. No. 7,037,191 B2, a change for the player to be involved in performance of the special game is provided to the player as an award in a case where the symbols stopped to be displayed form a predetermined combination. In the special game, 12 choices are displayed on the display of the slot machine. Then, the player selects one of the choices. When the result of the choice satisfies a predetermined condition, a high game value is given to the player. In other words, according to thus configured slot machine, a player can have a change for acquiring a high game value by playing the special game.
In slot machines, as a special game provided as the content of an award, so called a “free game” other than the game disclosed in the document U.S. Pat. No. 7,037,191 B2 has been known. In this free game, when a predetermined condition is satisfied, a same bet mode as the previous bet mode (that is, a bet mode used at a time when the predetermined condition is satisfied) is set and a slot game is performed without consuming any game value. Since a player can acquire an award during the free game without spending any game value by playing the free game, the free game is advantageous to the player.
As described above, since the bet mode of the free game is set on the basis of the previous bet mode, the player cannot be involved in the free game at all. In other words, during the free game, the player only watches symbols variably displayed and symbols stopped to be displayed.